H2—O2(air) fuel cells are well known in the art and have been proposed as a power source for many applications. There are several types of H2—O2 fuel cells including acid-type, alkaline-type, molten-carbonate-type, and solid-oxide-type. So called PEM (proton exchange membrane) fuel cells (a.k.a. SPE (solid polymer electrolyte) fuel cells) are of the acid-type, potentially have high power and low weight, and accordingly are desirable for mobile applications (e.g., electric vehicles). PEM fuel cells are well known in the art, and include a “membrane electrode assembly” (a.k.a. MEA) comprising a thin, proton transmissive, solid polymer membrane-electrolyte having an anode on one of its faces and a cathode on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements which (1) serve as current collectors for the anode and cathode, and (2) contain appropriate channels and/or openings therein for distributing the fuel cell's gaseous reactants over the surfaces of the respective anode and cathode catalysts. A plurality of individual cells are commonly bundled together to form a PEM fuel cell stack.
In PEM fuel cells hydrogen is the anode reactant (i.e., fuel) and oxygen is the cathode reactant (i.e., oxidant). Accordingly, the anode side of the fuel cell stack is supplied with hydrogen or a gas containing hydrogen and the cathode side is supplied with air. During the conversion of the anode reactant and cathode reactant to electrical energy, the fuel cell produces anode and cathode effluents. The anode side is typically operated in a “dead head” mode wherein the anode affluent is not continuously exhausted from the fuel cell stack. With this type of operation, nitrogen accumulates in the anode side of the fuel cells as a result of the diffusion through the MEA. Additionally, water also accumulates in the anode side. The accumulation of water and nitrogen results in a reduction in the operational level of the fuel cells and the voltage stability of the individual fuel cells of the fuel cell stack. This accumulation is typically concentrated in localized portions of the anode side of the fuel cells and, as a result, can cause the reduction in the operational level and the voltage stability of the fuel cells to occur quickly. This localized accumulation causes the reduction in the operational level and the voltage stability of the fuel cell before the remaining portion of the fuel cell is affected.
In order to reduce the nitrogen and water accumulations in the anode side, the anode side is flushed with anode reactant while the anode effluent is being vented from the anode side. However, the flushing of the anode side with the anode reactant leads to an anode effluent that contains a large quantity of hydrogen and therethrough leads to a higher hydrogen consumption. Thus, there is a need to address the accumulation situation.